The present invention relates to a device for controlling the timing needed to align the tip position of an image formed on the photoreceptive drum with the tip position of the copying paper in a zooming electrophotographic copying machine in which the magnification ratio is freely adjusted.
When operating any conventional electrophotographic copying machine, it is necessary to correctly align the tip position of the image formed on the photoreceptive drum with the tip position of the copy paper before forming the original image on the photoreceptive drum and thereafter transferring the image from the drum to the predetermined position of the copying paper. If the travelling scanner could detect its arrival at the tip position of the original paper, since the photoreceptive drum rotates at a constant speed, the tip position of the image on the drum can be aligned with the tip position of the copy paper at the transference position. In a copying machine which is provided with an actual-size magnification ratio, the original scanner travels at a constant speed. Thus, the scanner reaches the tip position of the original paper from the home position at a constant time. As a result, when operating a copying machine provided with the mechanisms mentioned above, the paper-feeding time can be controlled so that the tip position of the copy paper can reach the transference position exactly at the moment obtained by adding the time in which the scanner reaches the tip position of the original paper via its home position and the time needed for the image when the scanner reaches the tip position of the original paper, to move from the drum to the transference position. Conversely, when operating a copying machine which is capable of providing several magnification ratios, depending on the ratio, the travelling speed of the scanner varies. Accordingly, the time needed for the scanner to arrive at the tip position of the original paper via its home position also varies.